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Someone on bluesky recommended this as a good supplement to other Japanese language learning resources.

These hubs connect grammar concepts to give you a deeper understanding of how Japanese works. Learn the ins and outs of Japanese word types, conjugations and forms, and how culture affects communication.

In the same thread, Tae Kim's Guide to Japanese was mentioned as well.

Dan Abramov, the OP, also recommended using Kana on iOS for practicing Hiragana and Katakana.